1. Field of the Invention
The invention in general relates to steam turbine control systems and more particularly to a control system having redundant features coupled with a manual backup.
2. Description of the Prior Art
A variety of turbine control systems exist which utilize a central digital computer to govern steam admission by control of a plurality of steam admission valves, as well as stop and interceptor valves in those systems which include a reheater section between a high pressure and lower pressure turbine stage.
The centralized computer is responsive to various operating parameters to generate the necessary control signals, and, to provide for more reliable service, systems have been proposed which utilize both a primary and a redundant computer as well as a manual backup system. These centralized systems tend to be extremely complex and present difficulties in field servicing. The complexity is significantly increased if capabilities other than basic control are required, thus limiting the expansion capabilities of the control system.
In such turbine control systems an operator's panel is generally provided for operator interaction with the system with the panel including both a manual section and an automatic section. Any servicing of the automatic section requires the complete shutting down of the automatic control mode and a switching to the manual mode of operation just to perform the panel servicing.
While in a manual backup mode, the steam admission valve drive circuits receive control signals as dictated by the operator. These signals generally go to some common logic circuitry and then to the valve controllers such that a failure in the common logic circuitry prevents the valve controller from operating properly.
Overspeed protection control functions are generally provided in such systems for shutting down the valves or tripping the turbine system depending upon the degree of overspeed. A failure of this control circuit or a miscalculation in speed could result in undesirable operation of the system.
The above numerated difficulties are significantly reduced or eliminated with the control system of the present invention.